what parts are you looking to paint on it? is it chrome now? Black? What year and model truck? I am sure that @TRPLXL2 can lead you down the right path. She has painted tons of things on her truck. I would take her advice if she gives it as she has learned the do's and don'ts of this.

I have moved this thread to the general tech sub forum to try to get more answers for you.

i just painted my grill on a newly acquired '96 Chevy G30 van. it was an all plastic grill and head light bezels. it was pretty easy and simple. if you have all plastic parts wash well in kitchen detergent (i used Dawn) first and let them dry. then sand them lightly with 220 grit. if you have any chips or dings patch and sand them down (i used testor's contour putty). after they're all sanded and smooth blow the dust off (i used the wife's hair dryer) and wipe them down with denatured alcohol. i painted them with rustoleum "universal" paints. like krylon fusion it bonds to plastic, but it also has it own primer. the paint is very easy to spray but a can does not go a long way. i suggest you purchase double your estimate so you don't find yourself running back to the store. after the paint dried i applied several coats of rustoleum matte clear spray. test this stuff before you use it. i was not real happy with the results. i thought it would go on smoothly and just dull the sheen, but it went on very grainy. still all and all i am pleased with the outcome.
ps: i used a satin black for the base coat & forged hammered black for the trim.

ahhh no, but close maybe. i have an estimate from a local Line-X dealer to do the whole exterior in black bed liner for about 2/3's the cost of a quality paint job. a little more if i want to add color tint.